Aviation flight simulators are highly useful training tools for developing and improving flying skills. A modern flight simulator can include the full complement of instrumentation and controls used in flying an aircraft. The student's control inputs are converted into appropriate corresponding electrical signals and are fed into aircraft modeling apparatus, such as a programmed microcomputer. The modeling apparatus, in turn, generates appropriate corresponding aircraft response signals to be applied to the various indicating instruments, and the student adjusts his controls accordingly.
The flight characteristics of a wide variety of different flying conditions can be simulated by appropriate programming. A student pilot can use the simulator for practicing different fundamental maneuvers and procedures. An advanced student can practice the same maneuvers with one or more simulated emergencies, and experienced pilots can practice realistic approaches into airports into which they have never before flown.
The yoke assembly is one of the most important controls used in general aviation aircraft. The yoke assembly typically comprises a U-shaped steering yoke, analogous to the steering wheel of a car, attached to one end of an elongated shaft. Using the yoke, the pilot can rotate the shaft in either direction or move it axially inward (toward the nose) or outward.
The yoke shaft is rotationally coupled to the ailerons on the wings and axially coupled to the elevators on the tail. Clockwise rotation of the yoke and shaft lift the left aileron and lower the right so that the aircraft tends to turn in the direction the open "U" points. Similarly, counterclockwise rotation turns the plane in the opposite direction. Pushing the yoke and shaft axially inward lowers the tail elevators, pushing the nose of the aircraft down, and pulling the yoke out raises the elevators, raising the nose.
The yoke assembly is typically coupled to the ailerons and elevators by cable arrangements, and the pilot typically "feels" through the yoke assembly rotational and axial restoration forces very nearly proportional to the displacement of the ailerons and elevators from their respective equilibrium positions. In other words, the wind forces acting on the ailerons tend to rotate the yoke back to its centered position, and wind forces on the elevators tend to push the yoke shaft back to an equilibrium or resting position.
In order to alleviate the axial restoration forces for periods of prolonged climb or descent, aircraft typically includes a trim adjustment mechanism whereby secondary control surfaces on the elevators are used to counterbalance the wind force on the primary control surfaces. By properly adjusting the secondary control surface through a trim "wheel" or knob, the pilot can adjust the equilibrium axial position to correspond to a desired angle of climb or descent.
Prior attempts to simulate the response characteristics of the yoke assembly in a flight simulator have been less than satisfactory. Typical simulated yoke assemblies comprise a yoke, a shaft, a spring and a pair of potentiometers coupled to the shaft by gear trains. Despite the fact that the rotational and axial restoration forces encountered in flight are separate and independent of one another, typical prior art simulators have simulated both restoration forces by the same spring, resulting in cross-coupling. In other words, the force tending to rotationally center the yoke is not only dependent on the amount by which the yoke has been rotated but is also improperly dependent on the amount by which the shaft has been pushed in or pulled out. The consequence of this cross-coupling is that the simulator did not accurately communicate to the student the mechanical response of the yoke.
In addition, typical prior art simulators did not simulate the trim adjustment mechanism and its effect on the yoke assembly restoration force. Thus they failed to provide training in the use of this important control and further deviated from actual flight characteristics.
One further disadvantage of prior art simulators arises from their use of gear train assemblies to couple the shaft and potentiometers. The gear trains tend to produce side loading on the potentiometer shafts, pushing the shafts laterally to the side as well as rotating them. Such side loading contributed to premature failure of the potentiometers.
Another prior art yoke assembly simulator dispenses with gear drive chains by coupling the yoke shaft to the potentiometer shaft through a long pivotally mounted arm. The difficulty with this arrangement, however, is that it takes up a substantial amount of space in the simulator console normally occupied by the horizontal situation indicator in an actual aircraft. Thus, in order to use this coupling arrangement, the situation indicator must either be dispensed with or placed in a new location remote from its actual location in an aircraft.